1. Field of the Invention
The present invention relates to a resection guide, and more particularly to a resection guide which will ensure the correct orientation of the osteotomy cut of the head of the humerus with respect to the humeral intramedullary canal.
2. Description of the Prior Art
The humerus is the longest and largest bone of the upper limb, extending from the shoulder joint to the elbow joint where it articulates with the radius and ulna of the forearm. The proximal end of the humerus includes the humeral head which articulates with the glenoid cavity of the shoulder in a ball and socket fashion. The humeral head is nearly hemispherical in form.
As a result of certain diseases, such as rheumatoid arthritis, the humeral head may become so badly damaged that it must be resected and replaced with a prosthetic device. An acute fracture of the humeral head may also require its replacement with a prosthesis.
The prostheses typically used for this purpose include a stem portion designed to extend into the intramedullary canal of the humerus and a head portion designed to replace the humeral head. The head portion of the prosthesis extends angularly from the stem portion. The osteotomy cut of the natural humeral head must be made so that the angle of the cut corresponds to the angle between the stem and head portions of the prosthesis. In addition, the rotation of the cut varies to adjust to bone wear or capsulor looseness.
The humeral head osteotomy cut is currently being made free hand. The elbow of the patient is flexed to 90.degree. with the patient's forearm aimed at the midline of the operating surgeon's trunk. The humerus is externally rotated 30.degree. to 35.degree. to provide the recommended degree of retrotorsion in relation to the axis of elbow motion. The osteotomy is directed away from the surgeon, allowing the surgeon to reproduce the desired retrotorsion in the bone cut. A trial prosthesis may also be placed along the proximal humeral shaft as a guide for the proper inclination of the osteotomy.
The possibility for error exists with this free hand or "eyeball" approach. Inaccurate resection, even by a small amount, can result in an ill-fitting prosthesis which may cause complications for the patient and may eventually require replacement of the prosthetic device. Accordingly, the need exists for a humeral cutting guide which will ensure an exact and precise resection of the humeral head.